The bar-bellied sea snake is the longest of all sea snake species, growing up to two metres in length.

The bar-bellied sea snake forages for prey over sand flats, but is known to take shelter in seagrass beds to avoid predation by tiger sharks.

The diet of the bar-bellied sea snake may include fish and squid, but some studies suggest that this species is a specialist predator, feeding only on eels.

The female bar-bellied sea snake produces an average of 12 to 13 young per clutch, but some clutches have been reported to contain up to 30 young.

The bar-bellied sea snake is classified as Least Concern (LC) on the IUCN Red List (1). In addition, this species is included in the European Union’s Council Regulation (EC) No. 338/97, which protects species by regulating trade (2).

The longest of all sea snake species (1), the bar-bellied sea snake (Hydrophis elegans) can grow to an impressive length of up to two metres (2) (3), and is one of the most abundant Australian sea snakes (4). It is a venomous species (3) (4) (5) belonging to the largest genus of sea snakes, Hydrophis (6) (7), which comprises more than 30 species (7).

The bar-bellied sea snake has an elongated body (2) (8) (9), but while the neck and front part of the body are both slender (3) (9), the hind part of the body is very thick and is laterally compressed (2) (3) (8). A characteristic feature of sea snakes is the vertically flattened, paddle-like tail (10).

The colouration of the bar-bellied sea snake is highly variable throughout its range (1). Yellowish, fawn, brown or olive upperparts (3) (4) (8) give way to a paler underside (4) which is marked with a narrow, black band along its length (9). The head is grey, olive or black (2) (9), and this colouration is clearly separated from that of the body by a narrow white band (9).

Members of the Hydrophisgenus are also known as ‘banded sea snakes’ (6), and the bar-bellied sea snake is no exception. Its back is patterned with a series of broad, dark cross-bands or blotches (2) (3) (4) (8), which are thicker on the back and constricted towards the flanks (2) (9). In addition, the bar-bellied sea snake is marked with two rows of blotches or spots along each flank (2) (3) (4), with one of the rows being located in the pale interspaces between each of the main dorsal markings or ‘saddles’ (3) (4). The second row of spots is lower down on the flank, with each spot lying directly below a dorsal saddle (3) (4). The bar-bellied sea snake has a pale tail-tip, which helps distinguish it from some other Australian Hydrophis species (4).

The overlapping body scales of the bar-bellied sea snake are regular in shape (2) (3), and are either smooth (3) or have short keels (3) (9).

The bar-bellied sea snake occurs in the waters around Australia, Papua New Guinea, the Philippines and Indonesia (1) (5) (11). In Australia, where this species is widespread and particularly abundant (2) (11), the bar-bellied sea snake can be found from Shark Bay in Western Australia (2) through the waters of the Northern Territory, Queensland (2) (3) (5) and even down to central coastal New South Wales (3).

The bar-bellied sea snake’s range extends further into Australia’s temperate waters than that of most other sea snake species (1), and there have been reports of the species in the Burnett River, Queensland, although these are thought to be due to seasonal movements (2).

The bar-bellied sea snake lives in a range of marine habitats, particularly sandy and muddy habitats (1) (2) (12) in shallow coastal areas, tidal rivers and bays (8). It is also found in estuaries (2) (12) and, occasionally, coral reefs (1). Interestingly, the bar-bellied sea snake is also known to occur in freshwater habitats (1) (2), being found up to 12 kilometres upstream in the Burnett River, Queensland (2).

Although the bar-bellied sea snake is commonly found in water at depths of between about 3.7 and 26 metres (1), it has also been recorded at depths ranging from 2 to 80 metres (1) (2). The Queensland fishery has recorded this species reaching impressive depths of 110 metres (1).

In areas such as Shark Bay, Western Australia, the bar-bellied sea snake tends to forage over sand flats (13), but usually takes refuge and rests in seagrass beds at high tide (1) (13). While grassy areas limit the snake’s ability to forage for prey, they are thought to provide it with protection from tiger sharks (Galeocerdo cuvier), which are known to predate bar-bellied sea snakes and have access to most areas of the bay at high tide (13) (14).

The diet of the bar-bellied sea snake is reported to include squid, bottom-dwelling fish (1) (2) and eels (2) (3) (8). However, some studies suggest that, like other Hydrophis species, the bar-bellied sea snake may be a specialist predator, feeding only on eels (12) (13) (14) (15).

Despite being an air-breathing animal, the bar-bellied sea snake is capable of remaining underwater for up to two hours at a time, before surfacing to breathe again. Its single, elongated lung, which extends for almost the entire length of its body, is highly efficient for gas exchange, and sea snakes are also able to absorb oxygen through their skin when underwater. As in other sea snake species, the bar-bellied sea snake has specialised valves which block off its nostrils while underwater (2).

Living in the marine environment poses several other challenges, and like other sea snake species, the bar-bellied sea snake has a specialised gland under its tongue which enables it to excrete excess salt from its body. A sea snake sheds its skin approximately once every two to six weeks. By shedding its skin so frequently, a sea snake can get rid of the many marine species, such as algae and barnacles, which become attached to it (2).

Like most species of sea snake, the bar-bellied sea snake is viviparous (2) (5) (8) (15), meaning that it gives birth to live young rather than laying eggs (2). This species appears to reach sexual maturity at about two years old (2) (16), and females are thought to only breed every two to three years (1) (2) (16), although they may potentially breed every year (2).

Mating in sea snakes is a lengthy affair, and the males are unable to disengage from the female until copulation is complete (2). In northern Australia, mating takes place between early May and the end of July (2) (16). Although young are born in February in this region, bar-bellied sea snake births occur between March and May in southeast Queensland. Some studies suggest that the bar-bellied sea snake may move into estuaries to give birth (2).

The bar-bellied sea snake is thought to produce an average of about 12 or 13 young per clutch (1) (2) (16), although clutches of up to 30 young have been reported (2). Clutch size is also known to be variable and to increase with the length of the female (1).

The bar-bellied sea snake is abundant throughout its range, and is not considered to be at risk of extinction (1). However, it is known to be frequently caught as bycatch by trawl fisheries (1) (2), and in some areas, including the Gulf of Carpentaria, the bar-bellied sea snake is the most commonly captured species of sea snake (2). These air-breathing reptiles get caught in the trawl nets and often drown or become crushed by the weight of the catch (2). However, as a result of its wide distribution across most of northern Australia (1) and the fact that it has been found to have the lowest mortality rate from trawling of all the sea snakes tested (2), the bar-bellied sea snake may be more resilient to exploitation and the impact of bycatch than other species (1) (17).

Although there are currently no conservation measures in place specifically for the bar-bellied sea snake (1), this species, along with all other sea snakes in Australia, is nationally protected through its listing under the Environment Protection and Biodiversity Conservation Act 1999 (1) (2). The bar-bellied sea snake is found in the Great Barrier Reef Marine Park, which offers it some protection (1).

Marine Bioregional Plans have also been developed for four of Australia’s marine regions to improve understanding of Australia’s oceans, identify the conservation values of each marine region, and set out broad biodiversity priorities and objectives. As part of these plans, the bar-bellied sea snake has been identified as being of conservation value in the Temperate East, North and Northwest Marine Regions (2).

In addition, the Australian Fisheries Management Act 1991 requires fisheries to avoid impacting on protected or threatened species, including sea snakes. A three-year study has been set up to develop and implement a long-term bycatch monitoring programme for Australia’s Northern Prawn Fishery, which has the largest impact of any Commonwealth-managed fishery on protected sea snake populations. Since 2003, industry workshops have been jointly run by Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) and Australia’s Fisheries Management Authority (AFMA) to train prawn fishery crew members on how to identify, photograph and record information regarding sea snake capture during the main prawn seasons (1).

It has been recommended that further research be conducted into the design and placement of Bycatch Reduction Devices (BRD) (2) to reduce the impacts of trawling on sea snake populations (1) (2).

Find out more about sea snakes:

Carpenter, K.E. and Niem, V.H. (2001) The Living Marine Resources of the Western Central Pacific. Volume 6: Bony Fishes Part 4 (Labridae to Latimeriidae), Estuarine Crocodiles, Sea Turtles, Sea Snakes and Marine Mammals. Food and Agriculture Organization of the United Nations, Rome. Available at: ftp://ftp.fao.org/docrep/fao/009/y0870e/y0870e65.pdf

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk

Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.

Bycatch: in the fishing industry, the part of the catch made up of non-target species.

Dorsal: relating to the back or top side of an animal.

Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Gland: an organ that makes and secretes substances used by the body.

Keel: a projecting ridge along a flat or curved surface, particularly down the middle.

Viviparous: giving birth to live offspring that develop inside the mother’s body.